Renewable fuse



Sept. 12, 1950 A.' VISCHER, JR

RENEWABLE FUSE Filed Sept. 29, 1949 Patented Sept. l2, 1950 UNITED STATESl1 Parirrrv OFFICE RENEWABLE FUSE Alfred Vischer, Jr., Park Ridge, Ill. Application September 29, 1949, Serial No. v118,556

3 Claims. (NCI. 200-131) My invention relates generally to renewable fuses, and more particularly to improved ferrule type cartridge fuses having renewable fusible links.

In the ferrule type renewable link cartridge` fuses as at present commonly used, there is the ever present possibility that a person renewing the fusible link will fail tightly to clamp the link in place. If the link is not tightly clamped in position, there will be poor electrical contact between the parts of the fuse, with resultant high resistance and generation of heat. If the fuse is carelessly assembled, this contact may be so poor as to cause the fuse to heat up so rapidly that the fuse will blow prematurely. Even though the temperature rise resultant from the poor contact is not suflicient immediately to cause the fusible link to melt, the current carrying capacity of the fuse is lowered far below its rating and washer, which is so constructed and positioned that if the parts of the fuse are not tightly assembled to secure the desirable tight contact, any heat resultant from a poor connection will cause the bimetallic element to exert a force poration of this basic principle in the construction of fuses automatically eliminates overheating at points of mechanical and electrical contact, allowing fuses to operate cooler at maximum loads.

description, reference being had to the accompanying drawings, in which Fig. l is a part elevation and part central longitudinal sectional View of a fuse incorporating my invention;

Fig. 2 isa perspective view showing the fusible link and bimetallic washers;

Fig. 3 is a view similar to Fig. l, showing the fuse imperfectly assembled, and illustrating the operation of the bimetallic element to increase the contact pressure;

Fig. 4 is a fragmentary sectional view, taken on the line 4-4 of Fig. 1; and

Fig. 5 is a transverse sectional view, taken on the line 5-5 of Fig. 4.

Other objects will appear from the followingwgo .tending to increase the contact pressure. Incori,

The fuse comprises a tubular casing 6 of fiber or othersuitable insulating material, the ends of which are externally threaded to receive metallic ferrules 8 and I Il.'v yThe ferrules are provided with` internal annular flanges I2, which limit the extent to which the ferrule may be screwed upon the tubular casing 6. The outer end ofv each of the ferrules 8 and I6 is internally threaded to receive a plug I4, the latter being provided with a kerfy I6 to receive a screw driver and with an air vent opening I8.

As best shown in Fig. 2, the fusible member comprises a link 28- having a pair of portions 22, 24 of reduced cross sectional area, so that the portion of the link 20 therebetween will fall when the portions 22, 24` melt upon being subjected to an excessive current. The ends of the fusible link 26 are passed through slots 26 formed in contact discs 28, and have portions 30 bent to lie against the outer face of the contact discs.

The contact discs 28 are formed of a suitable bimetal having the metal of higher coeicient of expansion facing the end of the fuse.

In Fig. 4, for example, the layer 32 of the disc 28 will be composed of a metal having the higher `coeiiioient of expansion, while the layer 34 will befcomposed of a metal having a lower coefllcient of expansion. The vdiscs v28 are each provided with a lug 36 which is bentinwardly and adapted yto register with a suitable notch 38 formed in the flange I2 and a registering notch 42 formed in the end of the fiber casing 6, as best illustrated .in Figs. 4 and 5.-

The lug 36 prevents the disc from turning relative to the rferrule and makes it necessary that the disc ber inserted with the proper side facing outwardly. The lugs 36 are preferably of suilicient length that if they are incorrectly inserted in the ferrule (that is, upside down), the lugs will interfere with the insertion of the plugs I4, thus immediately indicating the error to the person endeavoring `to lassemble the fuse.

lThe lnotches 38 of the ferrules 8 and I0 are spaced degrees apart so that the fusible link 20 will extend diagonally across the casing 6. To prevent the ferrules from rotating after they have been screwed to the casing 6, they are staked thereto by having lugs 40 sheared from the flange I2 and pressed into the end of the iiber casing 6, as shown in Fig. 4. During this staking operation, the notch 38 may conveniently be formed in the flange I2 and the notch 42 pressed into the end of the ber casing 6 so as to be capable of receiving the lug 36 of the disc 28.

In Fig. l, the parts are shown as they would be properly assembled, the screw plug Il being threaded tightly in the ferrule 8 so that it lies ush with the end of the latter. When thus screwed in place, the screw plug will firmly contact with the bent over end portion 30 of the fusible link 20 and press the latter firmly against the disc 28. Under these circumstances a good electrical and mechanical contact will be made between the fusible link 20 and the ferrule 8, principally through the screw plug I4. However, even under such optimum conditions there will be slight heating of the ferrule due main ly to contact resistance, and this heating will result in a proportionately progressive increase in the contact pressure. That is, as the disc 28 becomes heated, it will tend to warp to the pc sition in which it is shown in Fig. 3, but being tightly confined between theilange I2 andthe screw plug IQ, the tendency of the discto warp will result merely in increased contactpressure between the end portion 3B of the fusible link 20 and the screw plug I4.

When the fuse is improperly assembled, as indicated in Fig. 3, as by failure to turn the screw plug Id rmly home, a very poor contact will be made between the end portion 30 of the fusible link and the screw plug I4. This poor contact will result in rapidly heating the disc 28, whereupon it will warp, as shown in Fig. 3, and firmly press the end portion 30 of the fusible link against the screw plug. This action will be very rapid and will take place before suicient heat'has been conducted to the fusible link to cause it to melt. In cartridge fuses of the type disclosed herein, but which do not employ the thermostatic bimetal washer, but instead use a slotted solid` brass washer, the normal heating of the fuse tends to expand the ferrule and this lessens the contact pressure between the screw plug and the end of the fusible link, and therefore causes the fuse to operate at excessively'high temperatures under maximum load conditions. If', on the other hand, a fuse were assembled in the careless manner indicated in Fig. 3, and the thermostatic bimetal disc were not used, the heat resultant from the poor contact would be rapidly communicated to the fusible link and the latter would melt even though the fuse was not subjectedto a current exceeding its rating.

Even though the fusible link did not melt, its resistance would be greatly increased and the wattage loss in the fuse would'be correspondingly increased. However, by introducing theA bimetal thermostatic disc 28, these disadvantageous eifects are obviated.

The diameter of the disc 28 relative to its thickness is suiiciently small that, with the ternperature changes encountered, the metalof the disc will not be stressed beyond its elastic limit, and therefore the disc will operate effectively throughout an indefinite period.

While I have shown my invention embodied in a cartridge fuse of the screw plug type, the

invention may likewise be embodied in fuses of the screw cap type.

It will be noted that the bimetal disc is heated mainly from the heat developed by a poor contact between the plug I4 and the end portion 30 of the fusible link, and not appreciably by the heat developed due to its resistance to the flow of electricity through it.

While I have shown and described a particular embodiment of my invention, I do not wish to be limited to the specific details which I have selected as illustrative, but desire to include within the scope of my invention all such variations and modifications as are defined by the claims which follow.

I claim:

l. A renewable link cartridge fuse comprising a tubular casing, a -ferrule secured to said casing. a fusible link, a bimetal disc for receiving the end portion of said link, and a plug threaded in said ferrule and arranged to press the end portion of said fusible link against said bimetal disc, said bimetal disc being arranged, when heated, to press the end portion of said fusible link against said plug with increased pressure.

2a A renewable link cartridge fuse comprising a casing, a contact member secured to said casing, a fusible link within said casing, a bimetal disc supporting one end of said fusible link, and an element removably secured to said member and pressing said end of said fusible link against said bimetal disc, said bimetal disc being arranged, upon an increase in temperature, to increase the contact pressure between said end of said fusible link and said clement.

3. In a renewable link cartridge fuse, the combination of a ferrule having a shoulder, a bin metal disc resting on said shoulder and having a slot for receiving the end of a fusible link, and means detachably secured to said ferrule for pressing the end portion of said fusible link against said disc, said bimetal disc tending, when heated, to deform in a direction to increase the pressure at its points of contact with the shoulder of the ferrule and with the end portion of the fusible link.

ALFRED VISCHER., J a.

REFERENCES CITED The following references are of record in the ille ofv this patent:

UNITED STATES PATENTS Number Name Date 1,180,767 Eustice Apr. 25, 1916 1,576,165 Weise Mar. 9, 1926 1,603,682 Gagnon Oct. 19, 1925 1,881,369 Carney Oct. fl, 1932 2,285,624 Tanner 'June 9, 1942 FOREIGN PATENTS Number Country Date 710,780 France June 9, 1931 '795,600 France Jan. 8, 1936 

